The present invention relates to a steering wheel for a power vehicle, which is formed as a telescopable pipe which is for example manually height adjustable.
More particularly, it relates to such a steering column of the above mentioned type, which has an inner pipe with at least one cast or molded sliding bush of synthetic plastic material or metal, and an outer pipe with pre-fabricated sliding surfaces.
Steering columns for power vehicles of the above mentioned general type are known in the art. One such steering column is disclosed for example in the German document DE-PS 3,202,669. In this reference the steering wheel is adjustable as to its height by a displacement force which is smaller than 100 N. In the above mentioned known steering wheel the inner pipe has a triangular cross-section and is provided with two sliding bushes in the overlapping region between the outer pipe and the inner pipe. The inner pipe is injection molded or cast with the sliding bushes in a mold. For obtaining a non-rotatable connection between the outer and inner pipes, the cylindrical outer pipe is shaped in accordance with the geometry of the sliding bushes in a partial region and fitted on the sliding bushes. For obtaining a play-free guidance of the outer and inner pipes in the region of the sliding bushes the pipe portion between the bushes is utilized and twisted as torsion bar, so that a sliding surface part of the inner pipe is pre-tensioned relative to the other part.
The pre-tensioning moment must be maintained within narrow limits. The lower limit is provided by the moment at the steering wheel, which must be transmitted in a play-free manner, and numbered in the passanger cars in the region with maximum 6 Nm. The upper limit is determined by the friction force produced by the pre-tensioning moment between the outer and the inner pipes. This value is dependent on sensation and in the manually height adjustable steering columns for power vehicles it is permitted to be maximum 120 N. Since a pre-tensioning moment of 6 Nm produced an adjusting force of approximately 85 N, lower adjusting forces in accordance with the above explained processes are not obtained. Since in the front-drive power vehicles in the case of fast straight drive short time torques due to street unevenness occur greater than 6 Nm, the play-free operation in this region is not achieved.